1. Field of the Invention
The present invention relates to a medical scanning system and a related method of scanning. More particularly, this invention relates to a medical scanning system and a related method that uses uniform rotary motion of an optical reflector to create reciprocal linear scanning.
2. Background of the Related Art
Various types of medical imaging techniques are currently used for diagnosis and treatment of a patient. These imaging techniques include ultrasound imaging and Optical Coherence Tomography (OCT). Ultrasound uses sound waves to obtain a cross-sectional image. These waves are radiated by a transducer and directed into the tissues of a patient. Waves reflected from tissues at different depths excite the same transducer, which now acts as a receiver. The transducer converts the reflected waves into electrical signals, which are electronically processed and ultimately displayed. The typical tissue depth applicable to ultrasound imaging varies, depending on the application, from millimeters to centimeters.
OCT uses electrical light to obtain a cross-sectional image of tissue. Since light waves are faster than sound waves, OCT takes a different approach to imaging. The depth of tissue scan in OCT is based on low coherence interferometry. Low coherence interferometry measures the field of an optical beam rather than its intensity. It preferably uses an interferometer with reference arm scanning and a low coherence light source. In use, a low coherence light source of the interferometer is directed onto a beam splitter to produce two beams, a sampling measurement beam and a reference beam. The sampling beam hits and penetrates the tissue or material to be imaged, and then reflects (backscatters) from the tissue, carrying information about the reflecting points from the surface and the depth of the tissue. The reference beam hits a reference reflector, for example a mirror or a diffraction grating, and reflects from the reference reflector. The reference beam travels a given path length, such that the reference reflector either moves or is designed such that the reflection occurs at different distances from the beam splitting point and returns at a different point in time or in space, which actually represents the depth scanning. The amount of such movement represents the desirable depth of penetration of the tissue or object being imaged by the sampling beam. Typical such depths in OCT are 2 to 3 millimeters.
The output of the interferometer is the superposition of the electromagnetic fields from the reflected reference beam and the sampling beam reflected from the tissue or material being imaged. When the reflected beams meet, interference is observed only where the path lengths of the reference arm and sampling arm are matched to within the coherence length of the light. A photodetector detects this interference and converts it into electrical signals. The signals are electronically processed and ultimately displayed, for example, on a computer screen or other monitor.
Each cross-sectional image involves two scans: depth (axial) and width (lateral). Typically, the rate of depth scan is faster than the rate of lateral scan, as 200 to 300 or more depth scans may occur for one lateral scan during live imaging. A typical rate of lateral scanning during live imaging is approximately 26-30 scans per second.
A typical OCT probe for linear cross sectional imaging uses a mechanical scanning arrangement in which at least one mechanical part reciprocates to create a scanning motion. The reciprocal motion, however, creates drawbacks associated with the inertia of moving parts. These drawbacks affect the accuracy of the scan. For example, reciprocal motion involves nonuniform speed of scan, i.e. the scanning speed decreases to zero at the end of each reciprocating cycle. In addition, vibration of the reciprocating mechanical parts results in an unstable scanning system and an elevated level of electronic noise. These problems increase as the scanning speed increases during live imaging.
In light of the drawbacks of the scanning systems described, there is a need for a scanning system which allows for better accuracy of scans at all speeds during live imaging. Accordingly, the present invention is directed to an improved device that obviates the limitations and disadvantages of conventional scanning systems.
To achieve these and other advantages and in accordance with the present invention, as embodied and broadly described herein, a scanning system is provided. The scanning system includes a light source for emitting a beam of light to be split into a reference beam and a sampling beam, a reference reflector for receiving and reflecting the reference beam, and a rotatable sampling reflector for receiving and reflecting the sampling beam.
In another embodiment of the invention, an imaging catheter is provided. The imaging catheter includes a catheter having a proximal end and a distal end, the catheter connected to a housing at the distal end of the catheter, the catheter including a light path for receiving and passing light from a light source, and a rotatable sampling reflector suspended within the housing so that the sampling reflector receives light from the light path.
According to one aspect of the invention, a method of scanning an object using optical coherence tomography. The method includes directing a light beam from a light source onto a rotating sampling reflector, reflecting the light beam off a surface of the rotating sampling reflector into an object to be scanned, and receiving the light beam reflected from the object.
Additional features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.